In the mining environment, minerals are sometimes excavated through the process of repetitive explosions. These explosions aid in exposing the ore, making it easier to collect and carry out on trucks for further processing at nearby facilities. However, the explosions also have a damaging effect upon the landscape of the mine. Continuous explosion blasts may cause steep slopes around the edges of the mine that are unstable and highly susceptible to avalanche type landslides. These landslides may cause serious injury to workers in the mine, destroy valuable equipment, or leave the ore burried under tons of rubble and, hence, unrecoverable.
Continuous monitoring of the slopes is required while a mine is being operated. Traditional methods of monitoring include stretching a taut wire along the surface of the slope, or using laser-based systems combined with a series of strategically placed prisms. Such methods are inefficient because they either require an inordinate amount of adjustments, or require trained personnel to visit the mine each time an adjustment is necessary.
Modern monitoring methods are able to make use of remote satellite-based positioning systems. The satellite system most commonly used today is the Global Positioning System (GPS). Engineering and monitoring methods which use GPS can be considerably more efficient and accurate than traditional methods. GPS utilizes signals transmitted by a number of in-view satellites to determine the location of a GPS mobile antenna which is connected to a receiver. The exact position of the antenna can then be monitored from a base station to determine whether there has been any movement of the position of the receiver.
Each GPS satellite transmits two coded L-band carrier signals which enable some compensation for propagation delays through the ionosphere. Each GPS receiver contains an almanac of data describing the satellite orbits and uses ephemeris corrections transmitted by the satellites themselves. Satellite to antenna distances may be deduced from time code or carrier phase differences determined by comparing the received signals with locally generated receiver signals. These distances are then used to determine antenna position. Only those satellites which are sufficiently above the horizon can contribute to a position measurement, the accuracy of which depends on various factors including the geometrical arrangement of the satellites at the time when the distances are determined.
Distances measured from an antenna to four or more satellites enable the antenna position to be calculated with reference to the global ellipsoid WGS-84. Local northing, easting and elevation coordinates can then be determined by applying appropriate datum transformation and map projection. By using carrier phase differences in any one of several known base or mobile receiver techniques, the mobile antenna coordinates can be determined to an accuracy on the order of .+-.1 cm. Using such real time kinematic (RTK) techniques, an operator can obtain position measurements within seconds of placing a mobile antenna on an unknown point. In RTK systems, GPS data is transmitted by a radio or other link between the base and mobile receivers, whether or not there is a dear line of site to ensure that accuracy in the mobile position measurements is maintained and the positioning information is correct.